Research paper
Efficient reduction of reactive black 5 and Cr(Ⅵ) by a newly isolated bacterium of Ochrobactrum anthropi

https://doi.org/10.1016/j.jhazmat.2020.124641Get rights and content

Highlights

  • A new strain from textile wastewater can effectively remove RB5 and Cr(Ⅵ).

  • The removal mainly occurs in the solution by bioreduction and biodegradation.

  • Additional electron donor and metal ion can enhance the removal of RB5 and Cr(Ⅵ).

Abstract

It is important to obtain bacteria with the ability for reduction of dyes and Cr(Ⅵ) since dyes and Cr(Ⅵ) are often co-exist in textile wastewater. In this study, a new strain belonging to Ochrobactrum anthropi was isolated from textile wastewater, and could efficiently reduce Reactive Black 5 (RB 5) and Cr(Ⅵ). The results showed the degradation efficiency of RB 5 could achieve 100% and reduction efficiency of Cr(Ⅵ) was up to 80% within 3 days at initial RB 5 and Cr(Ⅵ) concentration of 400 mg/L and 20 mg/L. Mn2+ and Cu2+ could enhance the removal of RB 5 and Cr(Ⅵ), respectively. Glycerin, as electron donor, improved reduction efficiencies of RB 5 and Cr(Ⅵ). In addition, reduction mechanisms were further investigated. The results demonstrated that decreasing of RB 5 and Cr(Ⅵ) concentration were mainly through extracellular bioreduction rather than by adsorption. The FTIR and XPS analyses revealed that the O‒H, C‒C and C‒H groups on the cell surface might be involved in the reduction of RB 5 and Cr(Ⅵ). The information gives useful insights into understanding of how the bacterium reduce RB 5 and Cr(Ⅵ). The results indicated that the strain had excellent application prospect for treating industrial wastewater.

Introduction

Textile industry is known to consume huge amount of water, moreover, 90% of the consumed water becomes wastewater (Pazdzior et al., 2019). At present, these wastewater has been a major environmental impediment for the development of the textile industry (Holkar et al., 2016). In China, the textile industry discharged as high as 1.84 billion tons of wastewater each year (Li et al., 2014, Chen et al., 2018, Li et al., 2016a, Li et al., 2016b). Dyes are the main organic pollutants in textile wastewater since about 15% of the dye cannot be completely utilized in the dyeing process (Joshi et al., 2020). Direct discharge of these wastewaters containing dyes not only causes undesirable aesthetic impact for water and decreases the photosynthesis as they impede penetration of light in water, but also can lead to severe health damage, such as tachycardia, cyanosis and tissue necrosis (Yang et al., 2018, Dafale et al., 2010). Azo dye accounts for about 80% of the dye used in the textile industry since its bright color and good chromaticity (van der Zee and Villaverde, 2005). Reactive Black 5 (RB 5) is a typical azo dye (Zheng et al., 2020). Besides, heavy metals like chromium and cobalt have been used to stabilize the color of dyes. Thus, heavy metals often co-exist with dyes in the textile wastewater (Kilic et al., 2007). Chromium is one of most abundant heavy metals, and mainly exist in the form of hexavalent (Cr(Ⅵ)), which shows higher toxicity than its trivalent form (Cr(III)). Moreover, Cr(Ⅵ) can easily pass the cell membrane, causing the damages of gastric canal, liver, kidney, and so on (Kilic et al., 2007, Wang et al., 2015, Ling et al., 2014, Ihsanullah et al., 2016). In addition, the allowable Cr(Ⅵ) level of 0.5 mg/L in industry wastewater has been strictly regulated by the integrated wastewater discharge standard (Das et al., 2013). Moreover, their co-existence can cause greater threat to the environment and human health (Desai et al., 2008a, Desai et al., 2008b). Therefore, it is very urgent and crucial to develop an efficient technique to simultaneously remove dyes and Cr(Ⅵ) from textile wastewaters (Dasgupta et al., 2015).

Many technologies have been adopted to treat the textile wastewaters, such as electrochemistry (Pan et al., 2019, Xia et al., 2020, Liu et al., 2020a, Liu et al., 2020b), membrane separation (Liu et al., 2020a, Liu et al., 2020b) and photocatalysis (Bahadori et al., 2020, El-Mekkawi et al., 2020). Although these technologies have been well documented, several defects such as secondary pollution, high manufactory cost and complex process flow are inevitable (Li et al., 2016b, Li et al., 2016a; Wang et al., 2021). Depending on the powerful metabolic ability of microorganisms, the pollutants can be completely mineralized or achieved low toxicity or non-toxicity conversion (Malaviya and Singh, 2016). Bioremediation have gained widespread attentions because it is considered as a cost-efficient and environment friendly technology for removing of pollutants from contaminated environments (Hayat et al., 2015).

It have been reported that many microorganisms could degrade RB 5, such as Enterobacter sp. (Wang et al., 2009) and Bacillus aryabhattai (Paz et al., 2017). These results demonstrated that oxygen, temperature, pH, concentration of dye, carbon and nitrogen sources, electron donor as well as redox mediator are significant factors which directly affect the microbial dye degradation. For example, the optimum pH for degradation is between 5.0 and 11.0 in range of 50–400 mg/L of dyes (Holkar et al., 2016). In addition, microbial degradation of azo dyes is mainly due to the reductive breakage of azo bonds (-N=N-) by azo-reductase enzymes under anaerobic condition (Masarbo and Karegoudar, 2020). Although the optimal conditions for dye degradation and the major degradation mechanisms have been discussed in previous studies, it is not very clear whether the degradation takes place inside or outside the cells and the distinction among different microorganisms (Mishra and Maiti, 2018).

Like biodegradation of dyes, many bacteria were found to own reduction ability of Cr(Ⅵ). For example, Streptomyces violaceoruber and Pseudomonas gessardii could reduce more than 92% of Cr(Ⅵ) within 48–144 h (Chen et al., 2014, Huang et al., 2016). Various factors have significant effects on the reducing efficiency, such as microbial species, aerobic or anaerobic condition, temperature, and so on. In general, Cr (Ⅵ) reduction is due to the (oxido)reductases produced by microorganisms such as aldehyde oxidase, nitroreductase, hydrogenases and DT-diaphorase, which may be intrecellular, extracellular and membrane (Wani et al., 2018, Julian-Sanchez et al., 2016).

It could be found that previous studies mainly focused on one issue of dye degradation and Cr(Ⅵ) reduction. This was not benefit to improve efficiency and decrease cost in the textile wastewater treatment, since it is inevitable to extend the process flow if dye degradation and Cr(VI) reduction were separately carried out (Louati et al., 2019). Therefore, it is very important to obtain microorganisms that can efficiently reduce both RB 5 and Cr(Ⅵ), which simplify the treatment process, as well as decrease the treatment cost.

In the present work, a bacterium capable of reducing RB 5 and Cr(Ⅵ) was isolated from textile wastewater. The reduction behaviors of RB 5 and Cr(Ⅵ) of the bacterium under different conditions were explored and the detailed reduction pathways of pollutants were also systematically studied.

Section snippets

Isolation and identification of microorganisms

The sample was obtained from an anaerobic reactor that treated textile wastewater. The reactor was originally inoculated with sludges collected from the Dongguan wastewater treatment plants (WWTPs) in Guangdong province, China. The operating temperature of the reactor was 30 ℃ and the pH value was 7.0. The serial dilution and the plate streaking were used to isolate microorganisms. The obtained pure culture was further identified according to its 16S rRNA gene sequences. Genomic DNA of the

Isolation and identification of the bacteria

A bacterial strain, named as S1, which had high reduction ability against Reactive Black 5(RB 5) and Cr(Ⅵ), was successfully isolated from textile wastewater. The 16S rRNA gene sequences similarity between strain S1 and Ochrobactrum anthropic strain MW6 (GenBank accession number: KT820200.1) was 99.93%, while 98% is considered as a reasonable threshold for identifying novel prokaryotic species (Richter and Rossello-Mora, 2009). Moreover, phylogenetic relationships based on 16S rRNA gene

Conclusions

The species of Ochrobactrum anthropi has not been previously reported to possess dual capabilities for reducing RB 5 and Cr(Ⅵ). In this work, a strain of Ochrobactrum anthropi S1 was successfully isolated and reported, which could efficiently reduce both RB 5 and Cr (Ⅵ). The RB 5 and Cr (Ⅵ) treatment behaviours at different conditions and reduction mechanisms were systemically investigated. The results suggested that the treatment of RB 5 and Cr(Ⅵ) mainly depended on bioreduction rather than

CRediT authorship contribution statement

Mingzhu Yuan conceived and designed the study and performed the experiments. Mingzhu Yuan and Zhenhua Mao wrote the paper. Haina Cheng, Hongbo Zhou, Hui Chen, Wenhao Zhan, Yuguang Wang and Qiang Zeng reviewed and edited the manuscript. All authors have given approval to the final version of the manuscript.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Project No. 31870115), the Open Funding Project of National Key Laboratory of Human Factors Engineering (No. 6142222190716 and SYFD061901K), Key Project of Research and Development of Hunan Province (No. 2018SK2043).

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